Investigating the Role of Subglacial Discharges and Changes in Cavity Geometry on Submarine Melting on Thwaites Glacier, West Antarctica

Abstract:

There is broad agreement that the sustained mass loss of Thwaites Glacier (TG), West Antarctica, over the last four decades has been primarily driven by the intrusion of warm Circumpolar Deep Water in its ice shelf cavity and in the grounding zone. The complex ocean circulation under the ice shelf, and resulting submarine melt, are the result of many factors such as tidal and Coriolis forces, buoyant flows (e.g., freshwater discharges), cavity geometry, bathymetric troughs, glacier and ocean properties, etc. In particular, subglacial freshwater discharge at the grounding line and changes in cavity geometry all have an effect on the pattern of submarine melt, but the individual role and contribution of each of these processes remains unclear. How the ocean circulation under the ice shelf and melting rate would be affected if the Eastern ice shelf collapses or if the flux of freshwater discharge increases is unknown, but could have potentially dramatic consequences on the mass balance of TG. Here, we employ a high-resolution regional ocean model (MITgcm) to investigate the impacts of these factors on the ocean circulation and resulting melting close to the grounding line of TG. We perform time-dependent numerical simulations for which we prescribe sources of freshwater discharges and changes the ice shelf cavity, and we compare with a control simulation where these factors are not changed. The subglacial discharge beneath TG is estimated by freshwater production due to basal slip and geothermal flux, and the spatial distribution of freshwater along the grounding line follows the bedrock topography. For cavity changes, we assume a hypothetical but likely scenario where a complete disintegration of the remaining TG ice shelf occurs rapidly and, consequently, exposing a large wall of ice to melting. While this scenario has consequences for the glacier flow itself, its impact on ocean-induced melt is not yet clear. Quantifying the effect of such factors helps guide ice-ocean modeling effort, which has been widely recognized as essential to forecast the mass loss of the West Antarctic Ice Sheet.